Hydrogen electrode reaction

Elving, P. J. Enyo, M. Critical Observations on the Measurement of Adsorption at Electrodes Mechanism of the Hydrogen Electrode Reaction as Studied by Means of Deuterium as a Tracer 7... 

Kita H. 2003. Horiuti s generahzed rate expression and hydrogen electrode reaction. J Mol Catal A 199 161-174. 

Petrii OA, Tsirlina GA. 1994. Electrocatalytic activity prediction for hydrogen electrode reaction intuition, art, sceince. Electrochim Acta 39 1739-1747. 

Takasu Y, Eujii Y, Yasuda K, Iwanaga Y, Matsuda Y. 1989. Electrocatalytic properties of ultra-fine platinum particles for hydrogen electrode reaction in an aqueous solution of sulfuric acid. Electrochim Acta 34 453-458. 

As mentioned previously, absolute potentials cannot be measured. Rather, potentials are measured against a reference electrode. The hydrogen electrode is perhaps the most common, and at standard conditions, it is defined to be 0 V. The hydrogen electrode reaction is... 

Fig. 2-44. Energy balance and electron energy levels in the normal hydrogen electrode reaction Ch- = standard gaseous proton level Estd = standard gaseous electron level.

Figure 6-5 shows an electrochemical cell of the redox reaction involving electron transfer coupled with a normal hydrogen electrode reaction. The cell diagram and cell reaction can be written, respectively, in Eqns. 6-13 and 6-14 ... 

For the electron transfer of hydrated redox particles (the outer-sphere electron transfer), the electrode acts merely as a source or sink of electrons transferring across the compact double layer so that the nature of the electrode hardly affects the reaction kinetics this lack of influence by the electrode has been observed for the ferric-ferrous redox reaction. On the other hand, the electron transfer of adsorbed redox particles (the inner-sphere electron transfer) is affected by the state of adsorption so that the nature of the electrode exerts a definite influence on the reaction kinetics, as has been observed with the hydrogen electrode reaction where the reaction rate depends on the property of electrode. 

As seen in Sect. 3.1, the transfer coefficient 0Erdey-Gruz and Volmer [32b] for the hydrogen electrode reaction, measures the symmetry of the free energy curves at this intersection in the transition state. In Fig. 5, it can be seen that the transfer coefficient determines the rate at which j grows exponentially with 77 for a constant n. 

On the other hand, among electrode reactions involving bond-breaking steps, theoretical approaches to the hydrogen electrode reaction have been extensively treated in the electrochemical literature [31, 41, 58— 62]. These reactions can be regarded as heterogeneous proton transfer processes. 

For the hydrogen electrode reaction (HER) on different metals, it is predicted that the curve log ja vs. AG ds has a maximum with log j0 decreasing both at positive and negative values of AGads. This is due to the opposite effects of the free energy of adsorption on the geometric and exponential factors in the electrokinetic equation (volcano plots). 

Platinum in the hydrogen electrode acts as a source or sink of electrons but does not take part in the reaction. It provides an electrical contact between H2 and the solution containing H+ ions and serves as a catalyst for the electrode reaction. Equilibrium between the hydrogen gas and H+ ions in this reaction is established slowly when a bright Pt (or Pd) is used. Equilibrium in the hydrogen electrode reaction is... 

In electrochemistry we have customarily employed, instead of the absolute electrode potential / abs scale, a relative scale of the electrode potential, E yila scale, referred to the standard or normal hydrogen electrode potential E m at which the hydrogen electrode reaction, 2H + 2e dox = H2(gas), is at equilibrium in the standard state unit activity of the hydrated proton, the standard pressure of 101.3 kPa for hydrogen gas, and room temperature of 298 K. Since Eniie is + 4.44 V (or + 4.5 V) in the absolute electrode potential scale, we obtain Eq. 9.9 for the relation between abs scile and [Refs. 4 and 5.] ... 

Fig. 9.7. An electrochemical cell consisting of a redox electrode reaction of hydrated ferric-ferrous ions and the standard hydrogen electrode reaction.

Connecting this ionic transfer reaction with the standard hydrogen electrode reaction + e( M) = (l/2)Hgives the cell shown in Fig. 9.8 and in Eq. 3.35 ... 

Fig. 9.8. An electrochemical cell consisting of an electrode reaction of iron ion transfer and the hydrogen electrode reaction both in equilibrium.

Electrode — Electrocatalytic electrode — Figure. Plots of the exchange current density of the hydrogen electrode reaction (left) as a function of the enthalpy of the metal-hydrogen bond and the current density of the electrochemical oxidation of ethylene as a function of the enthalpy of sublimation of various metals and alloys (right). These displays are also called Volcano plots... 

M. Enyo, Hydrogen electrode reaction on electrocatalytically active metals, in Comprehensive Treatise of Electrochemistry. Vol. 7, J. O M. Bockris, B. E. Conway, E. Yeager, and R. E. White, editors. Plenum Press, New York, 1983, pp. 241-300. 

Markovic NM (2003) The hydrogen electrode reaction and the electrooxidation of CO and H / CO mixtures on well-characterized Pt and Pt-bimetallic surfaces. In Vielstich W, Lamm A, Gasteiger HA (eds) Handbook of fuel cells fundamentals, technology and application, vol. 2 electrocatalysis. Wiley, Chichester, pp 368-393... 

Ludwig F, Sen RK, Yeager E (1977) Mechanism of the hydrogen electrode reaction on plah-num in acid solution. Elektrokhimiya 13 847... 

The major dehciency of the oxygen electrode reaction is its low exchange current density (about 10 A/cm on a smooth surface) in acid electrolytes on even the best-known electrocatalyst (a platinum-chromium alloy). This value is about six orders of magnitude lower than that for the hydrogen electrode reaction in the same electrolyte. The reaction is about three orders of magnitude faster on smooth platinum or nickel oxide surfaces in an alkaline medium as compared to acid. The... 

H. Kita, Periodic variation of exchange current density of hydrogen electrode reaction with atomic number and reaction mechanism, J. Electrochem. Soc. 113, 1095, 1966. 

Because electrochemical kinetic data are available only for the hydrogen electrode reaction (HER, H2/H+), the oxygen electrode reaction (OER, O2/H2O), and the hydrogen peroxide electrode reaction (HPER, H2O2/H2O), only H2, O2, and H2O2 are considered as the redox species in the MPM. The redox reactions of interest are therefore written as follows [35] ... 

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